There are a number of industrial applications requiring analysis of a mixed phase fluid. One example is the natural gas industry, where there is a need to analyze shale gas or wet gas comprising a natural gas as well as natural gas liquids and other liquids. Natural gases normally consist of methane and lesser amounts of other constituents, e.g., ethane and propane. Natural gas liquids typically comprise C4 hydrocarbons and heavier hydrocarbons. In the natural gas industry, it is quite often desired to determine the material composition of shale or wet gas flowing through a pipe, e.g., to determine its energy content. However, quantitative determinations of the energy content of mixed phase fluids require quantitative determinations of the material composition of the gas phase and the liquid phase. To this extent it is desirable not only to determine the presence of certain components comprised in the gas phase or the liquid phase of the fluid, but also the relative amounts or concentrations of these components of the composite fluid.
Conventionally, gas chromatographs have been applied to perform such multiphase analysis based on samples of the composite fluid taken at the industrial site. However, this approach has several disadvantages. Analysis methods performed with gas chromatographs require a rather complex sample handling system and, thus, are not capable of providing measurement results in real-time. In addition, such analysis requires modification of the temperature and the pressure of the mixed phase fluid samples, which may alter the composition of the analyzed material (i.e., the composite fluid). Consequently, a material composition determined based on such preprocessed samples may not reproduce the relative amounts or concentrations of the components in the mixed phase fluid correctly. In addition, shale or wet gases normally include a significant amount of water vapor as well as other gaseous components, like hydrogen sulfide, for example, which may impair the measurements or even damage the analyzer of the gas chromatograph. Thus, the samples must be dried and decontaminated, which renders the conventional method even slower and less reliable than it may otherwise be.
It is known in the art that the material composition of a gas or a liquid can be determined much faster by means of Raman spectroscopy. U.S. Pat. No. 7,385,692 B1 describes a Raman spectroscopic measurement system for determining gas concentrations in liquid receptacles. The disclosed system includes a Raman probe having a sensor tip inserted into the gas located above the liquid. The sensor tip includes a porous, gas-permeable cover preventing liquid from entering and interfering with the Raman spectroscopic measurement of the material composition of the gas inside the cover, which would otherwise cause the Raman scattered signal to be dominated by signal components emanating from the liquid, which do not represent the material composition of the gas.
U.S. Pat. No. 9,606,063 B2 describes a Raman spectroscopic measurement system for measuring the composition of a multi-phase flow fluid inside a high-pressure pipeline, the multi-phase flow fluid having a liquid-based multiphase flowing fluid chiefly located in the lower portion of the pipeline and a gas-based multiphase flowing fluid chiefly located in an upper portion of the pipeline. This system performs an analysis of the components and the composition of the gas-based multiphase flowing fluid using a first Raman probe installed in the upper portion of the pipeline. An analysis of the components and the composition of the liquid-based multiphase flowing fluid is performed using a second Raman probe installed in the lower portion of the pipeline. Accordingly, determining the material composition of the multi-phase flow fluid using this measurement system requires two separate Raman probes to be installed separately in two openings spaced along the pipeline. Two separate probes both increases installation costs and requires mounting means for each probe, each capable of not only holding the probe in place but also of properly sealing off the respective opening.
The Raman spectroscopic measurement system described in U.S. Pat. No. 9,606,063 B2 cannot be applied to analyze mixed phase fluids, e.g., mixed phase fluids ranging from thin aerosols to thick foams, where the gas phase is dispersed in the liquid phase or vice versa, because the Raman scattered signal received by the two Raman probes would both be dominated by Raman scattered signals emanating from the liquid phase. This makes it impossible or at least extremely difficult to extract sufficient information to truly account for the phase ratio of the liquid phase and the gas phase as well as for the material composition of the gas phase comprised in the fluid.
Accordingly, there remains a need for further contributions in this area of technology.